Thin polycrystalline silicon film forming method and thin film forming apparatus

ABSTRACT

A method of forming a thin polycrystalline silicon film and a thin film forming apparatus allowing inexpensive formation of a thin polycrystalline silicon film at a relatively low temperature with high productivity. More specifically, a method of forming a thin polycrystalline silicon film and a thin film forming apparatus in which a state of plasma is controlled to achieve an emission intensity ratio of hydrogen atom radicals (Hβ) of one or more to the emission intensity of SiH* radicals in the plasma. The thin film forming apparatus of a plasma CVD type includes a deposition chamber accommodating a deposition target substrate, a discharging electrode for plasma formation connected to a discharging power source, a gas supply device for supplying a gas and an exhaust device, and further includes an emission-spectrometer and a probe measuring device as well as a control portion for controlling at least one of the power supply, the gas supply and gas exhausting, for maintaining a desired state of plasma based on information detected by them.

TECHNICAL FIELD

[0001] The present invention relates to a method of forming a thinpolycrystalline silicon film by a plasma CVD method as well as a thinfilm forming apparatus which can be used for forming a thinpolycrystalline silicon film.

BACKGROUND ART

[0002] Thin silicon films have been used as a material for TFT (thinfilm transistor) switches arranged in pixels of liquid crystal displays,and have also been used for producing those such as various kinds ofintegrated circuits and solar batteries.

[0003] The thin silicon films are formed by a plasma CVD method usingsilane-containing reaction gases in many cases. Most of such thin filmsare thin amorphous silicon films.

[0004] A thin amorphous silicon film can be formed on a film depositionsubstrate which is kept at a relatively low temperature, and the thinfilm having a large area can be easily formed in a plasma of a materialgas produced by radio-frequency discharging (frequency: 13.56 MHz) usingelectrodes of a parallel plate type. Owing to the above, the thinamorphous silicon films have been widely used in switching devices forpixels of liquid crystal displays, solar batteries and the like.

[0005] However, an electric power generation efficiency of a solarbattery using a silicon film as well as characteristics such as aresponse speed of a semiconductor device using a silicon film cannotfurther be improved as long as an amorphous silicon film is used.Accordingly, it has been studied to utilize a thin crystalline siliconfilm such as a thin polycrystalline silicon film.

[0006] A thin crystalline silicon film such as a thin polycrystallinesilicon film can be formed by various methods, in which a filmdeposition substrate is kept at a temperature from 600° C. to 700° C.,such as CVD methods (e.g., a low pressure plasma CVD method and athermal CVD method), and PVD methods such as a vacuum vapor depositionmethod and a sputtering vapor deposition method. Also, the film may beformed, first by forming a thin amorphous silicon film at a relativelylow temperature by a method selected from various kinds of CVD and PVDmethods, followed then by a post-treatment of effecting a thermaltreatment at about 800° C. or more, or of effecting a thermal treatmentat about 600° for a long time.

[0007] Such a method is also known that laser annealing is effected onan amorphous silicon film for crystallizing it.

[0008] According to a method in which a substrate is subjected to a hightemperature, however, it is necessary to employ an expensive substratewhich can withstand a high temperature. For example, it is difficult toform a thin crystalline silicon film on an inexpensive glass substratehaving a low melting point (and a heat resistance temperature of 500° C.or less). Accordingly, a thin crystalline silicon film such as a thinpolycrystalline silicon film requires a high manufacturing cost.

[0009] According to a laser annealing method, a thin crystalline siliconfilm can be produced at a low temperature. However, a laser emittingstep is required, and laser light must be emitted with an extremely highenergy density. For those and other reasons, a manufacturing cost of athin crystalline silicon film becomes high.

[0010] Accordingly, an object of the invention is to provide a method ofmanufacturing a thin polycrystalline silicon film at a relatively lowtemperature with a low cost and a high productivity.

[0011] It is also an object of the invention to provide a thin filmforming apparatus, which can manufacture a thin polycrystalline siliconfilm at a relatively low temperature with a low cost and a highproductivity, and can furthermore be widely utilized for forming adesired thin film.

DISCLOSURE OF THE INVENTION

[0012] For achieving the above objects, the inventors made studies, andobtained the following knowledge:

[0013] A gas mixture, supplied into a film deposition chamber, of amaterial gas having silicon atoms [e.g., a silicon tetrafluoride (SiF₄)gas or a silicon tetrachloride (SiCl₄) gas] and a hydrogen gas or asilane-containing reaction gas [e.g., a mono-silane (SiH₄) gas, adisilane (Si₂H₆) gas or a trisilane (Si₃H₈) gas], supplied into a filmdeposition chamber, is decomposed by plasma formation so that a largenumber of decomposition products (various radicals or ions) are formed.Among the decomposition products, SiH₃*, SiH₂*, SiH* and the like arethe radicals that contribute to formation of a thin silicon film. Thestructure of the film, decided in the process of growth of the thinsilicon film, depends on a surface reaction on a substrate. It isconsidered that film deposition occurs as a result of reaction betweenuncombined hands of silicon atoms present on the substrate surface andthe radicals. For crystallizing the thin silicon film, it is necessaryto suppress as much as possible such a situation that silicon atomshaving uncombined hands or hydrogen atoms combined with silicon atomsare taken into the film. For that, it is considered important toincrease the covering rate of hydrogen atoms over the substrate surfaceand over the film surface formed thereon. Detailed mechanism is unknownon how hydrogen atoms covering the substrate surface and the filmsurface formed thereon suppress those such as hydrogen atoms combinedwith silicon atoms having uncombined hands taken into the film. However,it is considered that the uncombined hands of silicon atoms aresufficiently combined with hydrogen causing vaporization of them. Insummary, increase in the covering rate of hydrogen atoms over thesubstrate surface reduces silicon atoms having uncombined hands as wellas hydrogen atoms combined with silicon atoms taken into the substrate.For increasing the covering rate of hydrogen atoms over the substratesurface, it is essential that hydrogen atom radicals are always emittedfrom a plasma to the substrate. For this, it is important to increasethe density of hydrogen atom radicals in the plasma. According tostudies by the inventors, a thin polycrystalline silicon film of goodquality can be formed by increasing the density of hydrogen atomradicals so that the ratio of an emission intensity of hydrogen atomradicals (Hβ) to an emission intensity of SiH* radicals in the plasma,[i.e., (emission intensity of hydrogen atom radicals (Hβ))/(emissionintensity of SiH* radicals)] may be one or more.

[0014] The invention is based on the above knowledge, and provides athin polycrystalline silicon film forming method and a thin film formingapparatus described below.

[0015] (1) Thin Polycrystalline Silicon Film Forming Method

[0016] A method of forming a thin polycrystalline silicon film, in whicha plasma is formed from a gas mixture of a material gas having siliconatoms and a hydrogen gas, or from a silane-containing reaction gas, thestate of the-plasma is controlled to provide an emission intensity ofhydrogen atom radicals (Hβ) in the plasma exhibiting a ratio of one ormore to an emission intensity of SiH* radicals, and a thinpolycrystalline silicon film is formed on a substrate in the plasma.

[0017] (2) Thin Film Forming Apparatus

[0018] A thin film forming apparatus of a plasma CVD type including afilm deposition chamber for accommodating a deposition target substrate;a discharging electrode for plasma formation, in the film depositionchamber, connected to a discharging power source; a gas supply devicefor supplying a gas into the deposition chamber for film deposition; andan exhaust device for exhausting a gas from the deposition chamber,wherein the apparatus further includes an emission-spectrometer and aprobe measuring device for measuring the plasma state, and a controlportion for controlling at least one of a power supply from thedischarging power source (typically, a magnitude of the supplied power),a gas supply from the gas supply device (typically, a supplied gas flowrate) and exhausting by the exhaust device for maintaining apredetermined plasma state based on information detected from theemission-spectrometer and the probe measuring device.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 shows a schematic structure of an example of the thin filmforming apparatus according to the invention;

[0020]FIG. 2 shows a schematic structure of another example of the thinfilm forming apparatus according to the invention;

[0021]FIG. 3 shows an emission spectrum of SiH₄ plasma in theexperimental example 1 of the apparatus shown in FIG. 1 with an SiH₄supply amount of 10 ccm and a discharging power of 200 W;

[0022]FIG. 4 shows relationship between states of plasma [emissionintensity ratio (Hβ/SiH*) and ion density] and silicon crystallinitywith different supplied gas volumes and discharging power values forfilm deposition in the experimental example 1;

[0023]FIG. 5 shows relationship between Raman shift and Raman scatteringintensity obtained from laser Raman spectroscopy of a thin silicon filmin the experimental example 8 and also of a thin amorphous silicon filmin the prior art;

[0024]FIG. 6 shows a schematic structure of another example of the thinfilm forming apparatus according to the invention;

[0025]FIG. 7 is a flowchart showing operations of a control portion inthe thin film forming apparatus shown in FIG. 6;

PREFERRED EMBODIMENTS FOR IMPLEMENTING THE INVENTION

[0026] Preferred embodiments of the method of manufacturing a thinpolycrystalline silicon film and the thin film forming apparatusaccording to the invention are as follows;

[0027] (1) Method of Forming a Thin Polycrystalline Silicon Film

[0028] A plasma is formed from a gas mixture of a material gas havingsilicon atoms and a hydrogen gas, or from a silane-containing reactiongas. A state of the plasma is controlled to provide an emissionintensity of hydrogen atom radicals (Hβ) in the plasma exhibiting aratio of one or more to an emission intensity of SiH* radicals. A thinpolycrystalline silicon film is formed on a substrate in the plasma.

[0029] According to this thin polycrystalline silicon film manufacturingmethod, a thin polycrystalline silicon film of good quality is obtainedwith high productivity without a thermal post-treatment nor laserannealing required in the prior art.

[0030] According to the thin polycrystalline silicon film manufacturingmethod, the thin polycrystalline silicon film can be formed on asubstrate at a low temperature of 400° C. or lower. Accordingly, thesubstrate may be of an inexpensive substrate having a low thermalresistance such as an inexpensive glass substrate having a low-meltingpoint (heat-resistant temperature of 500° C. or lower). Thereby, thethin polycrystalline,silicon film can be manufactured at a low cost, andtherefore a liquid crystal display, a solar battery and varioussemiconductor devices utilizing the thin silicon films can be providedat a low cost.

[0031] The material gas having the silicon atoms may be, e.g., a silicontetrafluoride (SiF₄) gas or a silicon tetrachloride (SiCl₄) gas, and asilane-containing reaction gas may be a gas, e.g., of mono-silane(SiH₄), disilane (Si₂H₆) or trisilane (Si₃H₄).

[0032] A plasma state is controlled so that the ratio of an emissionintensity of hydrogen atom radicals (Hβ) to an emission intensity ofSiH* radicals in the plasma, i.e., (emission intensity of hydrogen atomradicals (Hβ))/(emission intensity of SiH* radicals) (hereafter referredto as Hβ/SiH*) may be equal to one or more. For this control, the stateof gas dissociation is measured by emission spectroscopy, and therebythe plasma state is controlled so that the emission intensity ofhydrogen atom radicals Hβ (emersion of 486 nm) may provide a ratio ofone or more to the emission intensity of SiH* (emersion of 414 nm) whichis one kind of radicals contributing to formation of the thin siliconfilm.

[0033] The upper limit of Hβ/SiH* can be large in a range not impedingformation of the thin polycrystalline silicon film, and is notparticularly restricted. However, although not restricted to this, theupper limit may be usually equal to about, 20 or less for preventingunpreferable ions from increasing, which is described later.

[0034] Control of the plasma state can specifically be performed bycontrolling at least one of a magnitude of the supplied electric powerfor plasma formation, a flow rate of the gas supplied into a depositionchamber, a deposition gas pressure in the deposition chamber and thelike.

[0035] For example, increase in supplied power (wattage) promotes gasdecomposition. However, excessive increase in supplied power results inunignorable increase in ions. A lower deposition gas pressure reducesions, but it also reduces hydrogen atom radicals. For example, in thecase of employing a gas mixture of a material gas having silicon atomsand a hydrogen gas, increase in amount of a supplied hydrogen gas canincrease the hydrogen atom radicals while suppressing increase in ions.In view of the above, a plasma is controlled to attain a desired plasmastate by appropriately controlling one or more of the magnitude of thesupplied power, the flow rate of the gas supplied into a depositionchamber, the deposition gas pressure in the deposition chamber and thelike.

[0036] When forming a thin polycrystalline silicon film, ions in theplasma are moved together with the radicals to the surface of thesubstrate as well as to the surface of the film being formed. However,increase in amount of injected ions damages the film being formed, andimpedes silicon crystallization, The injection energy of the ionsinjected from the plasma into the substrate surface is affected by theplasma potential, and is given by a difference between the plasmapotential and the substrate surface potential. According to studies bythe inventors, ion injection into the substrate can be suppressed to alarge extent by setting the plasma potential at 60 V or less. The numberof injected ions can also be reduced by controlling the plasma to reducethe density of ions produced in the plasma.

[0037] For controlling the plasma, the plasma potential may becontrolled to be equal to 60 V or less. Instead of this, or in additionto this, the plasma control may be performed to provide the ion densityof 5×10¹⁰ (cm⁻³) or less in the plasma.

[0038] The lower limit of the plasma potential is not particularlyrestricted unless it impedes formation of a thin polycrystalline siliconfilm, and may be, for example, although not restricted to this, equal toabout 10 V or more for obtaining the state allowing stable maintainingof the plasma.

[0039] It is preferable to decrease the density of ions produced in theplasma within a range not impeding formation of a thin polycrystallinesilicon film. For maintaining the stable plasma, it may be, for example,although not restricted to this, equal to about 1×10⁸ (cm⁻³) or more.

[0040] Typically, plasma formation can be performed in a dischargedsituation, in which case plasma formation using a cylindrical electrodeas the discharging electrode is more preferable than plasma formationusing a parallel plated electrode structure, i.e., a conventionalstructure, because the former can achieve more efficient gasdecomposition, and allows easy formation of plasma providing theemission intensity ratio (Hβ/SiH*) of 1 or more. This is because thesupplied gas must be decomposed efficiently for increasing the densityof the hydrogen atom radicals in the plasma to the extent providing theemission intensity ratio (Hβ/SiH*) of 1 or more, and gas decompositionis caused by collision in the plasma of fast electrons with gasmolecules. Electrons in the plasma, subject to changes of appliedvoltage, move between the electrodes, colliding with gas molecules.Accordingly, a conventional parallel plate type electrode structurecannot sufficiently promote gas decomposition because the distancebetween the electrodes is short, and electrons moving between theelectrodes do not so often collide with gas molecules. In contrast tothis, a cylindrical discharging electrode can decompose a gasefficiently by employing, as an opposed electrode, e.g., an inner wallof a deposition chamber or a substrate holder at the same potential asthe wall, and thereby increasing the distance between the electrodes toincrease the number of times of collision of moving electrons with gasmolecules. In the case of employing a cylindrical discharging electrode,it is arranged such that the center axis of the cylindrical form of thecylindrical discharging electrode is perpendicular or substantiallyperpendicular to the substrate surface.

[0041] Typically, plasma formation can be performed in a dischargedsituation, in which case a discharging power source used for dischargingfor plasma formation may be a radio-frequency power source of 13.56 MHzwhich has been generally used in the prior art. However, as thefrequency increases, electrons move more frequently per a unit timebetween electrodes, and gas decomposition occurs more efficiently.Therefore, the emission intensity ratio (Hβ/SiH*) can be easilyincreased by using a radio-frequency power source of, e.g., 60 MHz ormore.

[0042] Accordingly, plasma may be formed by discharging, and acylindrical electrode may be used as a discharging electrode fordischarging. In addition to, or instead of this, the discharging powersource used for discharging may be a radio-frequency power source of thefrequency of 60 MHz or more.

[0043] In the case where a radio-frequency power source of a frequencyof 60 MHz or more is used, the upper limit of the frequency is notparticularly restricted unless it impedes formation of a thinpolycrystalline silicon film. However, there is a tendency that anexcessively high frequency restricts a plasma generation region.Therefore, it may be substantially of the order of microwaves(typically, 2.45 GHz).

[0044] Hydrogen atom radicals produced by gas decomposition have a shortlifetime, and parts of them reach a substrate., However, the majority ofthem are recombined with neighboring hydrogen atom radicals or radicalsof, e.g., SiH₃*, SiH₂* or SiH*. Therefore, it is desired that the gaspressure during film deposition is low for suppressing such a situationthat the hydrogen atom radicals meet other radicals during movement to asubstrate. By employing the gas pressure of 20 m Torr or less, and morepreferably, of 10 m Torr or less, rather than the general depositionpressure range from hundreds of milli-torrs to several torrs, producedhydrogen atom radicals can efficiently reach a substrate.

[0045] Accordingly, the deposition gas pressure may be equal to 20 mTorr or less, or may be equal 10 m Torr or less. The lower limit of thedeposition gas pressure is not particularly restricted unless it impedesformation of a thin polycrystalline silicon film. It is preferably about0.1 m Torr or higher for smooth production and the like of plasma.

[0046] The substrate temperature during film deposition can be kept ator below 400° C. The lower limit of the substrate temperature duringdeposition is not particularly restricted unless it impedes formation ofa thin polycrystalline silicon film. Usually, the substrate temperatureis substantially equal to or higher than a room or an ambienttemperature around the film forming apparatus.

[0047] A description is now given again of the case relating toformation of a thin polycrystalline silicon film on a substrate, andmore specifically, of the case where a substrate is disposed in adeposition chamber, the internal pressure of the deposition chamber islowered to the deposition gas pressure by exhausting a gas therefrom,and plasma is formed by applying a radio-frequency power to thedeposition material gas, which is supplied into the deposition chamber,and is formed of a gas mixture of a material gas having silicon atomsand a hydrogen gas, or a silane-containing reaction gas. In this case ofthin polycrystalline silicon film formation, for example, the emissionintensity ratio (Hβ/SiH*) is set at 1 or more, and the plasma potentialVp is set at 60 V or less in the following manner.

[0048] When the emission intensity ratio is smaller than 1, and theplasma potential is equal to 60 V or less, the radio-frequency power isincreased. When the emission ratio is equal to 1 or more, and the plasmapotential is larger than 60, the degree of exhausting of the gas fromthe deposition chamber is controlled to increase the deposition gaspressure. When the emission intensity ratio is smaller than 1, and theplasma potential is larger than 60 V, the amount of the material gassupplied into the deposition chamber is reduced. In these manners, theconditions of the emission intensity of 1 or more and the plasmapotential of 60 V or less are attained. Some or all of these adjustmentmanners may be successively executed.

[0049] If the radio-frequency power is increased when the emissionintensity ratio is smaller than 1 and the plasma potential is 60 V orless, the degree of dissociation increases, and the emission intensityratio rises so that the emission intensity ratio changes toward 1 ormore without a change in plasma potential of 60 V or less.

[0050] When the amount of the gas exhausted from the deposition chamberis adjusted to increase the deposition gas pressure when the emissionintensity ratio is 1 or more, and the plasma potential is larger than 60V, energy supply from electric fields of respective ions decreases dueto decrease in average free path so that the plasma potential changestoward 60 V or less without causing a change in the emission intensityratio of 1 or more.

[0051] When the emission intensity ratio is smaller than 1 and theplasma potential is larger than 60 V, the amount of the material gassupplied into the deposition chamber may be decreased. Then, no longeris there lack of energy supplied to gas molecules due to excessive gassupply, and the emission intensity ratio changes toward 1 or more.Thereafter, the plasma potential may still be larger than 60 V. Then,the deposition gas pressure may be increased.

[0052] Control of the plasma state may be performed to attain the iondensity of the plasma not exceeding 5×10¹⁰ (cm⁻³) for forming a thinpolycrystalline silicon film.

[0053] Application of the radio-frequency power to the depositionmaterial gas may be performed by employing a cylindrical dischargingelectrode connected to the radio-frequency power source.

[0054] Application of the radio-frequency power to the depositionmaterial gas may be performed by employing a radio-frequency power ofthe frequency of 60 MHz or more.

[0055] The deposition gas pressure may be kept at or below 20 m Torr.

[0056] The substrate temperature during film deposition may be kept ator below 400° C.

[0057] (2) Thin Film Forming Apparatus

[0058] A thin film forming apparatus of a plasma CVD type including afilm deposition chamber for accommodating a deposition target substrate;a discharging electrode for plasma formation, in the film depositionchamber, connected to a discharging power source; a gas supply devicefor supplying a gas into the deposition chamber for film deposition; andan exhaust device for exhausting a gas from the deposition chamber,wherein the apparatus further includes an emission-spectrometer and aprobe measuring device for measuring the plasma state, and a controlportion for controlling at least one of a power supply from thedischarging power source (typically, a magnitude of the supplied power),a gas supply from the gas supply device (typically, a supplied gas flowrate) and exhausting by the exhaust device for maintaining apredetermined plasma state based on information detected from theemission-spectrometer and the probe measuring device.

[0059] According to this thin film forming apparatus, a depositiontarget substrate is disposed in a predetermined position in thedeposition chamber. The exhaust device operates to exhaust a gas fromthe deposition chamber. A gas for film deposition is supplied from thegas supply device, and discharging is performed from the dischargingelectrode to produce plasma from the gas thus supplied so that a film isformed on the substrate in the plasma. In this operation, the controlportion, operating based on information detected at theemission-spectrometer and the probe measuring device, controls at leastone of the electric power supply from the discharging power source, thegas supply from the gas supply device and exhausting by the exhaustdevice (control of gas supply from the gas supply device and ofexhausting by the exhaust device leads to control of the deposition gaspressure) so that the desired thin film can be formed.

[0060] For example, the gas supply device may be arranged to supply agas mixture of a material gas having silicon atoms [e.g., a silicontetrafluoride (SiF₄) gas or a silicon tetrachloride (SiCl₄) gas] and ahydrogen gas, or a silane-containing reaction gas [e.g., a mono-silane(SiH₄) gas, a disilane (Si₂H₆) gas or a trisilane (Si₃H₄) gas]. Further,the control portion may be arranged to control at least one of the powersupply from the discharging electrode, the gas supply from the gassupply device and exhausting by the exhaust device, so that hydrogenatom radicals (Hβ) in the plasma in the deposition chamber may provide adesired emission intensity ratio to the emission intensity of SiH*radicals according the emission-spectrometer, or the plasma potentialdetected by the probe measuring device may exhibit a predeterminedvalue, and thereby a predetermined thin silicon film (having apredetermined crystallinity and the like) may be formed on thesubstrate.

[0061] More specifically, for forming a thin polycrystalline siliconfilm on a substrate, the gas supply device may be arranged to supply amaterial gas having silicon atoms and a hydrogen gas, or asilane-containing reaction gas, and the control portion may be arrangedto control at least one of the power supply from the discharging powersource, the gas supply from the gas supply device and exhausting by theexhaust device so that hydrogen atom radicals (Hβ) in the plasma in thedeposition chamber may exhibit the emission intensity ratio of 1 or moreto the emission intensity of SiH* radicals according to theemission-spectrometer.

[0062] Alternatively, for forming a thin polycrystalline silicon film ona substrate, the gas supply device may be arranged to supply a materialgas having silicon atoms and a hydrogen gas, or a silane-containingreaction gas, and the control portion may be arranged to control atleast one of the power supply from the discharging power source, the gassupply from the gas supply device and exhausting by the exhaust deviceso that hydrogen atom radicals (Hβ) in the plasma in the depositionchamber may exhibit the emission intensity ratio of 1 or more to theemission intensity of SiH* radicals according to theemission-spectrometer, and the plasma potential measured by the probemeasuring device may not exceed 60 V. In this apparatus, the lower limitof the plasma potential is not particularly restricted unless it impedesformation of a thin polycrystalline silicon film, but may be equal toabout 10 V or more for stable maintaining or the like of the plasma,although not restricted to it.

[0063] In the latter case where control is performed to provide theemission intensity ratio of 1 or more, and the plasma potential of 60 Vor less, the discharging power source is formed of a radio-frequencypower source, and the control portion is arranged to provide theemission intensity ratio of 1 or more, and the plasma potential of 60 Vor less in the following manner. When the emission intensity ratio issmaller than 1, and the plasma potential is 60 V or less, theradio-frequency power source is controlled to increase the powersupplied therefrom. When the emission intensity ratio is 1 or more, andthe plasma potential is larger than 60 V, the exhaust device iscontrolled to adjust the amount of the gas exhausted from the depositionchamber for increasing the deposition gas pressure in the depositionchamber. When the emission intensity ratio is smaller than 1, and theplasma potential is larger than 60 V, the gas supply device may becontrolled to reduce the amount of the gas supplied into the depositionchamber.

[0064] In any one of the foregoing thin film forming apparatuses forforming the thin polycrystalline silicon films, the upper limit ofHβ/SiH* can be large in a range not impeding formation of the thinpolycrystalline silicon film, and is not particularly restricted asalready described. However, the upper limit may be equal to about 20 orless for preventing increase of unpreferable ions, which is to bedescribed later, although not restricted to it.

[0065] According to the thin film forming apparatus for forming the thinpolycrystalline silicon film, the thin polycrystalline silicon film ofgood quality can be formed with high productivity without performing athermal post-treatment and laser annealing required in the prior art.

[0066] The thin polycrystalline silicon film can be formed on asubstrate at a low temperature of 400° C. or lower. Accordingly, thesubstrate may be an inexpensive substrate having a low thermalresistance such as an inexpensive glass substrate having a low-meltingpoint (heat-resistant temperature of 500° C. or lower). Thereby, thethin polycrystalline silicon film can be manufactured at a low cost, andtherefore a liquid crystal display, a solar battery and varioussemiconductor devices utilizing the thin silicon films can be providedat a low cost.

[0067] In the case where the thin film forming apparatus is used forforming the thin polycrystalline silicon film, the thin film formingapparatus may have the following structures for the same reasons asthose already described in connection with the method of forming thethin polycrystalline silicon film. The thin film forming apparatus mayemploy two or more of the following features (a)-(d) in combinationunless a problem arises.

[0068] (a) The thin film forming apparatus for forming the thinpolycrystalline silicon film, wherein the control portion controls atleast one of the power supply from the discharging power source, the gassupply from the gas supply device and exhausting by the exhaust deviceso that the ion density of the plasma measured by the probe measuringdevice may exhibit a value of 5×10¹⁰ (cm⁻³) or less.

[0069] It is preferable to lower the density of ions produced in theplasma within a range not impeding formation of the thin polycrystallinesilicon film, and the density may be equal to, e.g., about 1×10⁸ (cm⁻³)or more from a viewpoint of, e.g., stable maintenance the plasma,although not restricted to it.

[0070] (b) The thin film forming apparatus for forming the thinpolycrystalline silicon film, wherein the discharging electrode is acylindrical electrode.

[0071] (c) The thin film forming apparatus for forming the thinpolycrystalline silicon film, wherein the discharging power source is apower source supplying a power of a frequency of 60 MHz or more.

[0072] The upper limit of the frequency of the discharging power sourceis not particularly restricted unless it impedes formation of the thinpolycrystalline silicon film. However, there is a tendency that anexcessively high frequency restricts a plasma generation region.Therefore, it may be substantially of the order of microwaves(typically, 2.45 GHz).

[0073] (d) The thin film forming apparatus for forming the thinpolycrystalline silicon film, wherein the control portion controls atleast one of the gas supply from the gas supply device and exhausting bythe exhaust device for maintaining the deposition gas pressure at 20 mTorr or less, or at 10 m Torr or less.

[0074] The lower limit of the deposition gas pressure is notparticularly restricted unless it impedes formation of the thinpolycrystalline silicon film, but is preferably equal to about 0.1 mTorr or more for smooth production and the like of the plasma.

[0075] More specific embodiments of the invention are described belowwith reference to the drawings.

[0076]FIG. 1 shows a schematic structure of an example of the thin filmforming apparatus according to the invention.

[0077] The thin film forming apparatus shown in FIG. 1 includes adeposition chamber (plasma producing chamber) 1, a substrate holder 2disposed in the chamber 1, a cylindrical discharging electrode 3arranged in the chamber 1 and located above the substrate holder 2, adischarging radio-frequency power source 4 (i.e., a radio-frequencypower source for discharging) connected to the discharging electrode 3via a matching box 41, a gas supply device 5 for supplying a gas forfilm deposition into the deposition chamber, an exhaust device 6connected to the deposition chamber for exhausting a gas from thedeposition chamber, an emission-spectrometer 7 and a probe measuringdevice 8 for measuring a state of a plasma formed in the depositionchamber, and a control portion 9 which controls at least one of thepower supplied from the power source 4, the gas supply from the gassupply device and the deposition pressure in the deposition chamberbased on information detected at the emission-spectrometer 7 and at theprobe measuring device 8 for obtaining a predetermined plasma state. Allof these components operate in accordance with instructions sent from ahost computer 100. In the figure, “11” indicates an intermediate hubdevice for governing the transmission and reception of signals.

[0078] The substrate holder 2 includes a heater 2H for heating thesubstrate.

[0079] The cylindrical discharging electrode 3 is disposed such that thecenter axis of its cylindrical form intersects substantiallyperpendicularly the central portion of a deposition target substrate Sdisposed on the substrate holder 2.

[0080] The power source 4 is a variable power source controlled by aninstruction from the control portion 9, and can supply a radio-frequencypower of a frequency of 60 MHz.

[0081] Both the deposition chamber 1 and the substrate holder 2 aregrounded.

[0082] The gas supply device 5 in this embodiment can supply amono-silane (SiH₄) gas, and includes a gas source of SiH₄ as well as avalve (not shown), a mass-flow controller 51 and the like. The mass-flowcontroller 51 controls a flow rate in accordance with an instructionfrom the control portion 9.

[0083] The exhaust device 6 includes an exhausting pump as well as avalve (a conductance valve in this embodiment) 61 and the like. Thevalve controls the exhausted gas flow rate in accordance with aninstruction from the control portion 9.

[0084] The emission-spectrometer 7 can detect the emission spectra ofproducts produced by gas decomposition for determining the ratio(Hβ/SiH*) of the emission intensity of the hydrogen atom radicals (Hβ)to the emission intensity of the SiH* radicals.

[0085] Hβ/SiH* is obtained by the following formula in view of thesensitivity calibration of the device:

Emission intensity ratio (Hβ/SiH*)=(lb×αb)/(Ia×αa)

[0086] la: emission intensity of SiH* (414 nm)

[0087] αa: calibration factor of 414 nm in the device

[0088] lb: emission intensity of Hβ (486 nm)

[0089] αb: calibration factor of 486 nm in the device

[0090] The probe measuring device 8 is a device for measuring the plasmastate by a Langmuir probe. The probe measuring device 8 can detectvoltage/current characteristics in the plasma, and can calculate fromthe detected characteristics the plasma potential, ion density, electrondensity and electron temperature.

[0091]FIG. 2 shows a schematic structure of another example of the thinfilm forming apparatus according to the invention.

[0092] The thin film forming apparatus shown in FIG. 2 is a plasma CVDdevice of a parallel plated electrode structure, and includes adeposition chamber (plasma producing chamber) 10, the substrate holder 2which is disposed in the chamber 10, is kept at the ground potential andis provided with the heater 2H, a plate-type discharging electrode 31disposed in the chamber 10 and located above the substrate holder 2, thedischarging radio-frequency power source 4 connected to the dischargingelectrode 31 via the matching box 41, the gas supply device 5 forsupplying the gas for film deposition into the deposition chamber, theexhaust device 6 connected to the deposition chamber for exhausting thegas from the deposition chamber, the emission-spectrometer 7 and theprobe measuring device 8 for measuring the plasma state produced in thedeposition chamber, and the control portion 9 which controls at leastone of the power supplied from the power source 4, the gas supply fromthe gas supply device 5 and the deposition pressure in the depositionchamber based on information detected at the emission-spectrometer 7 andat the probe measuring device 8 for obtaining the predetermined plasmastate. All of these components operate in accordance with instructionsfrom the host computer 100. In the figure, “11” indicates theintermediate hub device for governing the transmission and reception ofthe signals.

[0093] This apparatus is identical with that shown in FIG. 1 except forforms of the deposition chamber (plasma producing chamber) 10 and thedischarging electrode 31.

[0094] In either of the thin film forming apparatuses shown in FIGS. 1and 2, the deposition target substrate S is arranged on the substrateholder 2 in the deposition chamber, and is heated to a predeterminedtemperature, if necessary. The exhaust device 6 operates to exhaust agas from the deposition chamber while supplying a mono-silane gas fromthe gas supply device 5 into the deposition chamber. A plasma isproduced from the gas thus supplied by performing discharging from thedischarging electrode 3 (31) so that a film is formed on the substrate Sin the plasma thus produced. In this operation, the control portion 9controls at least one of the magnitude of the electric power suppliedfrom the discharging power source 4, the amount of the gas supplied fromthe gas supply device 5 and the deposition pressure set by adjusting thegas supply rate and/or the exhaust amount by the exhaust device 6. Thecontrol portion 9 performs the above control for providing apredetermined emission intensity ratio of hydrogen atom radicals (Hβ) toan emission intensity of SiH* radicals in the plasma in the depositionchamber according to measurement by the emission-spectrometer 7, or forfurther providing a predetermined plasma potential detected at the probemeasuring device 8. A predetermined thin silicon film (having apredetermined crystallinity and the like) can thus be formed on thesubstrate S.

[0095] In particular, the control portion 9 controls at least one of themagnitude of the electric power supplied from the discharging powersource 4, the amount of the gas supplied from the gas supply device 5and the deposition pressure set by adjusting the gas supply amountand/or the exhaust amount by the exhaust device 6 so that the emissionintensity of hydrogen atom radicals (Hβ) may exhibit a ratio of 1 ormore to the emission intensity of SiH* radicals in the plasma in thedeposition chamber according to measurement by the emission-spectrometer7, or further that the plasma potential detected at the probe measuringdevice 8 may not exceed 60 V. Thereby, a thin polycrystalline siliconfilm can be formed on the substrate S at the substrate temperature of400° C. or less with high productivity.

[0096] For more smooth forming of a thin polycrystalline silicon film ofhigh quality, the following may further be employed.

[0097] (a) The control portion 9 controls at least one of the magnitudeof the power supplied from the discharging power source 4, the amount ofthe gas supplied from the gas supply device 5 and the depositionpressure by adjusting the gas supply amount and/or the exhaust amount bythe exhaust device 6 so that the ion density in the plasma may exhibit avalue of 5×10¹⁰ (cm⁻³) or less.

[0098] (b) The control portion 9 controls the amount of the gas suppliedfrom the gas supply device 5 and/or the amount of the gas exhausted bythe exhaust device 6 so that the deposition gas pressure may not exceed20 m Torr and, more preferably, may not exceed 10 m Torr.

[0099] Experimental examples of formation of thin silicon films aredescribed.

EXPERIMENTAL EXAMPLE 1

[0100] A glass substrate was disposed on the substrate holder 2 of theapparatus using the cylindrical electrode 3 shown in FIG. 1, and theexhaust device 6 exhausted a gas from the deposition chamber 1 to attaina pressure of 2×10⁻⁶ Torr. Then, the exhausting operation was continued,and simultaneously the gas supply device 5 supplied 5 sccm ofmono-silane gas (SiH₄). Further, the power source 4 applied aradio-frequency of 60 MHz and 200 W to the cylindrical electrode 3 tocause discharging in the deposition chamber 1. Thereby, the plasma wasformed from the deposition gas, and a thin silicon film of 500 Å wasformed on the glass substrate. During this formation, the deposition gaspressure was kept at 2.0 m Torr, and the substrate temperature was keptat 400° C.

[0101] The crystallinity of the thin silicon film thus formed wasevaluated by a laser Raman spectroscopy, and it was confirmed that athin polycrystalline silicon film was formed. In the above Ramanspectroscopy, peaks of the crystalline silicon (Raman shift=515−520cm⁻¹) were detected with respect to the structure (Raman shift=480 cm⁻¹)of the amorphous silicon formed by a conventional plasma CVD method, andthereby the crystallinity was confirmed. The crystallinity evaluationwhich for the following examples is the same as the foregoing evaluationin the Raman spectroscopy.

[0102]FIG. 3 shows emission spectra of the SiH₄ plasma with the SiH₄supply amount of 5 ccm and the discharging electric power of 200 W. FIG.3 shows emission spectra corresponding to products produced by gasdecomposition, and more specifically shows that the SiH* contributing tosilicon deposition emitted the light of 414 nm, hydrogen atom radicals(Hβ) emitted the light of 486 nm, and a large number of and SiH* andhydrogen atom radicals were present in the plasma.

[0103] The emission intensity ratio (Hβ/SiH*) between the emissionintensity of hydrogen atom radicals (Hβ) and the emission intensity ofSiH* radicals (414 nm) was 1.10 (αa: 0.0145, αb: 0.0167), according tothe emission-spectrometer 7.

[0104]FIG. 4 shows a relationship between the state of plasma [theemission intensity ratio (Hβ/SiH*) and the ion density] and the siliconcrystallinity with various values of the gas supply amount and thedischarging power for forming the film according to the experimentalexample 1. From FIG. 4, it is seen that the thin polycrystalline siliconfilm was obtained with the emission intensity ratio (Hβ/SiH*) of 1.0 ormore regardless of the ion density, as shown by solid circles. When theemission intensity ratio (Hβ/SiH*) was smaller than 1.0, the thinamorphous silicon film was formed as shown by blank squares in FIG. 4.Increase in ion density impeded crystallization, and a higher emissionintensity ratio (Hβ/SiH*) was required for crystallization. Therefore,it is understood that the ion density of 5×10¹⁰/cm³ or less is desiredfor efficiently obtaining a thin polycrystalline silicon film.

EXPERIMENTAL EXAMPLES 2 and 3

[0105] In the experimental example 2, a thin silicon film was formed bythe thin film forming apparatus shown in FIG. 1. In the experimentalexample 3, another thin silicon film was formed by the thin film formingapparatus shown in FIG. 2.

[0106] Deposition Conditions of Experimental Example 2 Substrate glasssubstrate SiH₄ Supplied Amount  5 sccm Discharging Power  60 MHz, 300 WSubstrate Temperature 400° C. Deposition Gas Pressure  2 m Torrmaintaining stable discharging Deposited Film Thickness 500 Å

[0107] Deposition Conditions of Experimental Example 3 Substrate glasssubstrate SiH₄ Supplied Amount  5 sccm Discharging Power  60 MHz, 300 WSubstrate Temperature 400° C. Deposition Gas Pressure 150 mTorrmaintaining stable discharging Deposited Film Thickness 500 Å

[0108] The crystallinity of the thin silicon films obtained in theexperimental examples 2 and 3 were evaluated by the Raman spectroscopy.In the experimental example 2, formation of a thin polycrystallinesilicon film was confirmed, and formation of a thin amorphous siliconfilm was confirmed in the experimental example 3. The emission intensityratio (Hβ/SiH*) in the plasma was 1 or more in the experimental example2, and was smaller than 1 in the experimental example 3.

EXPERIMENTAL EXAMPLES 4 and 5

[0109] Experimental examples 4 and 5 were performed from a viewpoint ofa frequency of the radio-frequency power.

[0110] In the experimental example 4, a thin silicon film was formed bythe thin film forming apparatus shown in FIG. 1. In the experimentalexample 5, another thin silicon film was formed by a thin film formingapparatus shown in FIG. 1 with a replaced discharging power source 4 of13.56 MHz and 300 W in this example.

[0111] Deposition Conditions of Experimental Example 4 Substrate glasssubstrate SiH₄ Supplied Amount  5 sccm Discharging Power  60 MHz, 300 WSubstrate Temperature 400° C. Deposition Gas Pressure  2 m TorrDeposited Film Thickness 500 Å

[0112] Deposition Conditions of Experimental Example 5 Substrate glasssubstrate SiH₄ Supplied Amount    5 sccm Discharging Power 13.56 MHz,300 W Substrate Temperature   400° C. Deposition Gas Pressure    2 mTorr Deposited film Thickness   500 Å

[0113] The crystallinity of the thin silicon films obtained in theexperimental examples 4 and 5 were evaluated by the Raman spectroscopy.In the experimental example 4, formation of a thin polycrystallinesilicon film was confirmed, and formation of a thin amorphous siliconfilm was confirmed in the experimental example 5. The emission intensityratio (Hβ/SiH*) in the plasma was 1 or more in the experimental example4, but was smaller than 1 in the experimental example 5 due to the lowdischarging frequency of 13.56 MHz.

EXPERIMENTAL EXAMPLES 6 and 7

[0114] Experimental examples 6 and 7 were performed from a viewpoint ofthe deposition gas pressure.

[0115] In either of the experimental examples 6 and 7, a thin siliconfilm was formed by the thin film forming apparatus shown in FIG. 1.

[0116] Deposition Conditions of Experimental Example 6 Substrate glasssubstrate SiH₄ Supplied Amount  5 sccm Discharging Power  60 MHz, 300 WSubstrate Temperature 400° C. Deposition Gas Pressure  2 m TorrDeposited Film Thickness 500 Å

[0117] Deposition Conditions of Experimental Example 7 Substrate glasssubstrate SiH₄ Supplied Amount  5 sccm Discharging Power  60 MHz, 300 WSubstrate Temperature 400° C. Deposition Gas Pressure  50 m TorrDeposited film Thickness 500 Å

[0118] The crystallinity of the thin silicon films obtained in theexperimental examples 6 and 7 were evaluated by the Raman spectroscopy.In the experimental example 6, formation of a thin polycrystallinesilicon film was confirmed, and formation of a thin amorphous siliconfilm was confirmed in the experimental example 7. The emission intensityratio (Hβ/SiH*) in the plasma was 1 or more in the experimental example6, but was smaller than 1 in the experimental example 7 due to the highdeposition pressure of 50 m Torr. Further, the ion density of the plasmain the experimental example 7 was higher than that in the experimentalexample 6.

EXPERIMENTAL EXAMPLE 8

[0119] A thin silicon film was formed by the apparatus shown in FIG. 2.

[0120] Deposition conditions are as follows: Non-alkali glass substrateand Substrate Si-Wafer <100> SiH₄ Supplied Amount  30 sccm DischargingPower  60 MHz, 800 W Hβ/SiH*  2.5 Plasma Potential  45 V ElectronTemperature  2.3 eV Deposition Gas Pressure  1 × 10⁻³ Torr SubstrateTemperature 400° C. Deposited Film Thickness 500 Å

[0121] The hydrogen concentration and the crystallinity of the thinsilicon films thus produced were evaluated by FT-IR (Fourier TransformInfrared Spectroscopy) and the laser Raman spectroscopy.

[0122] Regarding the FT-IR, the hydrogen concentration of the film wasquantitatively determined from the Si—H (Stretching-band) absorptionpeak integrated intensity of 2000 cm⁻¹. The determined value was 5×10²⁰cm⁻³ or less, which was significantly reduced and improved as comparedwith a value of 2×10²² cm⁻³ exhibited by a conventional specimen(amorphous silicon film).

[0123]FIG. 5 shows a relationship between a Raman shift and a Ramanscattering intensity by a laser Raman method of the thin silicon filmformed in the experimental example 8 and of a thin amorphous siliconfilm in the prior art.

[0124] According to the result of the crystallinity evaluation in theRaman spectroscopy, a peak (Raman shift=515−520 cm⁻¹) of thecrystallized silicon was detected to the conventional specimen(amorphous silicon structure, Raman shift=480 cm⁻¹), and thecrystallinity of the thin silicon film was confirmed. Presence ofcrystal grains of 100 Å-2000 Å in diameter was confirmed.

[0125] In addition to the experimental example 8 described above, thinsilicon films were formed in such manners that various different valuesof plasma control parameters, namely, discharging power, supplied gasflow rate and deposition gas pressure, were employed in the experimentalexample 8, but Hβ/SiH* of 1 or more and the plasma potential notexceeding 60 V were maintained. In any one of the cases, the values ofFT-IR were significantly reduced and improved as compared with 2×10²²cm⁻³ of the conventional specimen (amorphous silicon film) Further,presence of a thin polycrystalline silicon film was confirmed accordingto the Raman spectroscopy.

[0126] Further another example of the thin film forming apparatusaccording to the invention is described with reference to FIG. 6.

[0127] The thin film forming apparatus in FIG. 6 is a plasma CVD deviceof a parallel plated electrode structure substantially same as the thinfilm forming apparatus in FIG. 2. The apparatus in FIG. 6 includes adeposition chamber (plasma producing chamber) 10′, the substrate holder2 which is disposed in the chamber 10′, is kept at the ground potentialand is provided with the heater 2H, the plate-type discharging electrode31 disposed in the chamber and located above the substrate holder 2, thedischarging radio-frequency power source 4 connected to the dischargingelectrode 31 via the matching box 41, the gas supply device 5 forsupplying a gas for film deposition into the deposition chamber, theexhaust device 6 connected to the deposition chamber for exhausting thegas from the deposition chamber, the emission-spectrometer 7 and theprobe measuring device 8 for measuring a state of a plasma formed in thedeposition chamber, and the control portion 9′ which controls powersupplied from the power source 4, the gas supply from the gas supplydevice 5 or the deposition pressure (deposition gas pressure) in thedeposition chamber based on information detected at theemission-spectrometer 7 and the probe measuring device 8 for obtaining apredetermined plasma state. The apparatus is also provided with asubstrate shutter ST which is driven by a drive portion D between aposition for covering the substrate S disposed on the holder 2 and anescaped position exposing the substrate S. All of these componentsoperate in accordance with instructions from the host computer 100. Inthe figure, “11” indicates the intermediate hub device for governing thetransmission and reception of the signals.

[0128] The power source 4 is a variable power source controlled by aninstruction from the control portion 9′, and can supply aradio-frequency power of a frequency of 60 MHz.

[0129] The gas supply device 5 in this embodiment is to, supplymono-silane (SiH₄) gas, and includes, e.g. a gas source of SiH₄ as wellas a valve (not shown), a mass-flow controller 51, which controls anamount of the gas supplied to the deposition chamber 10′ by controllingthe flow rate in accordance with an instruction from the control portion9′.

[0130] The exhaust device 6 includes, e.g. an exhausting pump as well asa valve 61 (a conductance valve in this example) for controlling anexhausting rate or amount in accordance with an instruction from thecontrol portion 9′, and thereby controlling the deposition pressure(deposition gas pressure) in the deposition chamber 10′.

[0131] The shutter drive portion D drives the shutter in accordance withan instruction from the control portion 9′.

[0132] The emission-spectrometer 7 is similar to theemission-spectrometer shown in FIGS. 1 and 2, can detect emissionspectra of products from gas decomposition, and includes a memory forstoring detected emission intensities of SiH* radicals and hydrogen atomradicals (Hβ), and an operating portion for obtaining the emissionintensity ratio (Hβ/SiH*) by arithmetic operations from the respectiveemission intensities stored in the memory.

[0133] In this example, Hβ/SiH* is likewise obtained by the followingformula in view of the sensitivity calibration of the device: Emissionintensity ratio (Hβ/SiH*)=(lb×αb)/(Ia×αa)

[0134] The probe measuring device 8 is a device for measuring a plasmastate by a Langmuir probe similarly to the probe measuring devices shownin FIGS. 1 and 2, and includes an operating portion for obtaining aplasma potential from probe-measured data by arithmetic operations.

[0135] In the thin film forming apparatus shown in FIG. 6, thedeposition target substrate S is disposed on the substrate holder 2 inthe deposition chamber 101, and is initially covered with the shutterST. If necessary, it is heated to a predetermined temperature, and theexhaust device 6 operates to exhaust the gas from the depositionchamber. At the same time, the gas supply device 5 supplies amono-silane gas into the deposition chamber, and discharging from thedischarging electrode 31 is performed so that a plasma is produced fromthe gas. The control portion 9′ performs the control as follows.

[0136] As shown in the flowchart of FIG. 7, the control portion 9′ readsthe emission intensity ratio (Hβ/SiH*) obtained by theemission-spectrometer 7, and also reads the plasma potential Vp detectedby the probe measuring device 8 (step S1).

[0137] Further, the control portion 9′ determines whether the conditionsof (Hβ/SiH*)≧1 and Vp≦60 V are satisfied (step S2). When satisfied, thecontrol portion 9′ moves the shutter ST to expose the substrate S bysending an instruction to the drive portion D, and starts the deposition(step S3).

[0138] When the foregoing conditions are not satisfied, operations areperformed in the following order.

[0139] First, it is determined whether the conditions of (Hβ/SiH*)<1 andVp≦60 V are satisfied or not (step S4).

[0140] If YES, the output (wattage) of the power source 4 is increasedby a predetermined magnitude (step S5).

[0141] If NO, it is determined whether the conditions of (Hβ/SiH*)≧1 andVp>60 V are satisfied or not (step S6). If YES, the exhaust regulatingvalve 61 of the exhaust device 6 is operated to increase the gaspressure in the deposition chamber 10′ by a predetermined amount (stepS7). When NO, the conditions of (Hβ/SiH*)<1 and Vp>60 V are present sothat the mass-flow controller 51 of the gas supply device 5 is operatedto decrease the gas supply amount by a predetermined amount (step S8).

[0142] After increasing the power output, the deposition chamber gaspressure or the gas supply amount by a predetermined degree or amount inthe step S5, S7 or S8, the process returns to the step S1 for readingdetected information from devices 7 and 8, and it is determined whetherthe detected information satisfies the conditions of (Hβ/SiH*)≧1 andVp≦60 V. If necessary, similar steps are repeated.

[0143] When the conditions of (Hβ/SiH*)≧1 and Vp≦60 V are satisfied inthe above manner, the drive portion D is instructed to move the shutterST. Thereby, the substrate S is exposed, and deposition starts.

[0144] Through the above steps, a thin polycrystalline silicon film canbe formed with high productivity on the substrate S at the substratetemperature of 400° C. or less.

[0145] For forming a thin polycrystalline silicon film of high qualitymore smoothly, the device shown in FIG. 6 may be arranged as follows;

[0146] (a) For achieving the ion density of the plasma not exceeding5×10¹⁰ (cm⁻³), the control portion 9′ may control at least one of themagnitude of the supplied power from the discharging power source 4, theamount of the gas supplied from the gas supply device 5 and thedeposition pressure, which can be controlled by controlling the suppliedgas amount and/or the exhausted gas amount by the exhaust device 6.

[0147] (b) The control portion 9 may control the supplied gas amountfrom the gas supply device 5 and/or the exhausted gas amount by theexhaust device 6 so that the deposition gas pressure may not exceed 20 mTorr, and more preferably 10 m Torr.

[0148] By using the thin film forming apparatus shown in FIG. 6, a thinpolycrystalline silicon film of high quality was formed on the samesubstrate as that in the foregoing experimental example 8 by settingsubstantially the same conditions as the experimental example 8.

[0149] Industrial Applicability

[0150] The invention can be applied to forming thin polycrystallinesilicon films on processing target objects such as a display substrateof a liquid crystal display, substrates of various integrated circuitsand a substrate of a solar battery by a plasma CVD method.

1. A thin polycrystalline silicon film forming method, in which a plasma is formed from a gas mixture of a material gas having silicon atoms and a hydrogen gas, or from a silane-containing reaction gas, the state of said plasma is controlled to provide an emission intensity of hydrogen atom radials (Hβ) in the plasma exhibiting a ratio [(emission intensity of hydrogen atom radicals (Hβ))/(emission intensity of SiH* radicals)] of one or more to an emission intensity of SiH* radicals, and a thin polycrystalline silicon film is formed on a substrate in the plasma.
 2. The method of forming a thin polycrystalline silicon film according to claim 1, wherein said plasma is controlled to provide a plasma potential of 60 V or less.
 3. The method of forming a thin polycrystalline silicon film according to claim 1 or 2, wherein said plasma state is controlled to provide an ion density of 5×10¹⁰ (cm⁻³) or less for forming the thin polycrystalline silicon film.
 4. The method of forming a thin polycrystalline silicon film according to claim 1, 2 or 3, wherein said plasma is formed by discharging, and a discharging electrode used for discharging is a cylindrical electrode.
 5. The method of forming a thin polycrystalline silicon film according to any one of the preceding claims 1 to 4, wherein said plasma is formed by discharging, and a discharging power source used for discharging is a radio-frequency power source of a frequency of 60 MHz or more.
 6. The method of forming a thin polycrystalline silicon film according to any one of the preceding claims 1 to 5, wherein a deposition gas pressure is kept at 20 m Torr or less.
 7. The method of forming a thin polycrystalline silicon film according to any one of the preceding claims 1 to 6, wherein a substrate temperature is kept at 400° C. or less during deposition.
 8. The method of forming a thin polycrystalline silicon film according to claim 2, wherein for forming a thin polycrystalline silicon film on said substrate, said substrate is disposed in the deposition chamber, the internal pressure of said deposition chamber is lowered to the deposition gas pressure by exhausting the gas therefrom, and said plasma is formed by applying a radio-frequency power to the deposition material gas supplied into the deposition chamber, formed of the gas mixture of the material gas having the silicon atoms and the hydrogen gas, or the silane-containing reaction gas; when said emission intensity ratio is smaller than 1, and said plasma potential is equal to 60 V or less, said radio-frequency power is increased; when said emission intensity ratio is 1 or more, and said plasma potential is larger than 60 V, the exhausting amount of the gas from the deposition chamber is adjusted to increase said deposition gas pressure; when said emission intensity ratio is smaller than 1, and said plasma potential is larger than 60 V, the amount of said material gas supplied into said deposition chamber is reduced, thereby the conditions of the emission intensity ratio of 1 or more and the plasma potential of 60 V or less are set.
 9. The method of forming a thin polycrystalline silicon film according to claim 8, wherein said plasma state is controlled to provide the ion density of the plasma equal to 5×10¹⁰ (cm⁻³) or less for forming the thin polycrystalline silicon film.
 10. The method of forming a thin polycrystalline silicon film according to claim 8 or 9, wherein a cylindrical discharging electrode connected to a radio-frequency power source is employed for applying said radio-frequency power to said deposition material gas.
 11. The method of forming a thin polycrystalline silicon film according to any one of the preceding claims 8 to 10, wherein a radio-frequency power of a frequency of 60 MHz or more is used as said radio-frequency power applied to said deposition material gas.
 12. The method of forming a thin polycrystalline silicon film according to any one of the preceding claims 8 to 11, wherein the deposition gas pressure is kept at 20 m Torr or less.
 13. The method of forming a thin polycrystalline silicon film according to any one of the preceding claims 8 to 12, wherein the substrate temperature is kept at 400° C. or less during deposition.
 14. A thin film forming apparatus of a plasma CVD type including a film deposition chamber for accommodating a deposition target substrate; a discharging electrode for plasma formation in said deposition chamber connected to a discharging power source; a gas supply device for supplying a gas for film deposition into said deposition chamber; and an exhaust device for exhausting a gas from said deposition chamber, wherein further included are an emission-spectrometer and a probe measuring device for measuring the plasma state, and a control portion for controlling at least one of the power supply from said discharging power source, the gas supply from said gas supply device and exhausting by said exhaust device, for maintaining a predetermined plasma state based on information detected at said emission-spectrometer and said probe measuring device.
 15. The thin film forming apparatus according to claim 14, wherein said gas supply device can supply a material gas having silicon atoms and a hydrogen gas, or a silane-containing reaction gas, said control portion can control at least one of the power supply from said discharging power source, the gas supply from said gas supply device and exhausting by said exhaust device so that hydrogen atom radicals (Hβ) in the plasma in the deposition chamber may provide an emission intensity ratio [(emission intensity of hydrogen atom radicals (Hβ))/(emission intensity of SiH* radicals)] of one or more to the emission intensity of SiH* radicals according to said emission-spectrometer, for forming a thin polycrystalline silicon film on said substrate.
 16. The thin film forming apparatus according to claim 14, wherein said gas supply device can supply a material gas having silicon atoms and a hydrogen gas, or a silane-containing reaction gas, said control portion controls at least one of the power supply from said discharging power source, the gas supply from said gas supply device and exhausting by said exhaust device so that hydrogen atom radicals (Hβ) in the plasma in the deposition chamber may provide an emission intensity ratio [(emission intensity of hydrogen atom radicals (Hβ))/(emission intensity of SiH* radicals)] of one or more to the emission intensity of SiH* radicals, according to said emission-spectrometer, and also a plasma potential obtained by said probe measuring device may exhibit 60 V or less, for forming a thin polycrystalline silicon film on said substrate.
 17. The thin film forming apparatus according to claim 16, wherein said discharging power source is a radio-frequency power source; when said emission intensity ratio is smaller than 1, and said plasma potential is 60 V or less, said power supplied from said radio-frequency power source is increased by said control portion, when said emission intensity ratio is 1 or more, and said plasma potential is larger than 60 V, the amount of exhausted gas by said exhaust device from the deposition chamber is adjusted to increase the deposition gas pressure in the deposition chamber by said control portion; when said emission intensity ratio is smaller than 1, and said plasma potential is larger than 60 V, the amount of gas supplied into the deposition chamber from said gas supply device is reduced by said control portion; and thereby the conditions of the emission intensity ratio of 1 or more and the plasma potential of 60 V or less are set, for forming a thin polycrystalline silicon film on said substrate.
 18. The thin film forming apparatus according to claim 15, 16 or 17, wherein said control portion controls at least one of the power supply from said discharging power source, the gas supply from said gas supply device and exhausting by said exhaust device so that the ion density of the plasma obtained by said probe measuring device may be 5×10¹⁰ (cm⁻³) or less.
 19. The thin film forming apparatus according to any one of the preceding claims 15 to 18, wherein said discharging electrode is an cylindrical electrode.
 20. The thin film forming apparatus according to any one of the preceding claims 15 to 19, wherein said discharging power source is a power source supplying an electric power of a frequency of 60 MHz or more.
 21. The thin film forming apparatus according to any one of the preceding claims 15 to 20, wherein said control portion controls at least one of the gas supply from said gas supply device and exhausting by said exhaust device for maintaining deposition gas pressure at 20 m Torr or less. 